1. Field of the Invention
The present general inventive concept relates to an inkjet printhead, and more particularly, to a heater which can control a shape of a bubble generated in an inkjet printhead to enhance capability of ink ejection, and an inkjet printhead including the heater.
2. Description of the Related Art
An inkjet printhead is an apparatus that ejects minute ink droplets on desired positions of recording paper in order to print predetermined color images. Inkjet printers are classified into a shuttle type inkjet printer having a printhead being shuttled in a direction perpendicular to a transporting direction of a print medium to print an image, and a line printing type inkjet printer having a page-wide array printhead corresponding to a width of the print medium. The line printing inkjet printer has been developed for realizing high-speed printing. The array printhead has a plurality of inkjet printheads arranged in a predetermined configuration. In the line printing type inkjet printer, the array printhead is fixed while the print medium is transported during printing, thereby enabling the high-speed printing.
Inkjet printheads are categorized into two types according to an ink droplet ejection mechanism thereof. The first one is a thermal inkjet printhead that ejects ink droplets due to an expansion force of ink bubbles generated by thermal energy. The other one is a piezoelectric inkjet printhead that ejects ink droplets by a pressure applied to ink due to deformation of a piezoelectric body.
The ink droplet ejection mechanism of the thermal inkjet printhead is as follows. When a current flows through a heater made of a heating resistor, the heater is heated and ink near the heater in an ink chamber is instantaneously heated up to about 300° C. Accordingly, ink bubbles are generated by ink evaporation, and the generated bubbles are expanded to exert a pressure on the ink filled in the ink chamber. Thereafter, an ink droplet is ejected through a nozzle out of the ink chamber.
FIG. 1 is a cross sectional view illustrating a conventional thermal inkjet printhead. Referring to FIG. 1, the conventional inkjet printhead includes a substrate 10 on which a plurality of material layers are formed, a chamber layer 20 stacked on the substrate 10, and a nozzle layer 30 stacked on the chamber layer 20. An ink chamber 22 filled with ink to be ejected is formed in the chamber layer 20 and a nozzle 32 through which ink is ejected is formed in the nozzle layer 30. In addition, the substrate 10 has an ink feed hole 11 to supply ink to the ink chamber 22.
A typical silicon substrate is used as the substrate 10. An insulating layer 12 for insulation between a heater 13 and the substrate 10 is formed on the substrate 10. The insulating layer 12 is typically made of silicon oxide. The heater 13 is formed on the insulating layer 12 to heat the ink of the ink chamber 22 and generate a bubble. An electrode 14 is formed on the heater 13 to apply current to the heater 13.
A passivation layer 15 is formed on the heater 13 and the electrode 14 to protect the heater 13 and the electrode 14. The passivation layer 15 is typically made of silicon oxide or silicon nitride. An anti-cavitation layer 16 is formed on the passivation layer 15. The anti-cavitation layer 16 protects the heater 13 from a cavitation force generated when the bubbles vanish and is typically made of tantalum (Ta).
In the conventional inkjet printhead, the heater has a constant resistance in each portion and thus the amount of the heat generated in each portion of the heater 16 is the same. Accordingly, the conventional inkjet printhead including the heater 13 cannot control a shape of the bubble generated by the heater 13. Thus it is difficult to improve the capability of the ink ejection. Moreover, the bubble generated by the heater 13 is expanded to an ink inlet through which ink is flown to the ink chamber 22, and thus a back flow of the ink in the ink chamber 22, that is, ink flowing back to the ink inlet, may occur.